With development of vehicle technology, interpersonal distance is reduced and human's life quality is improved. Vehicles drove by oil have an engine using liquid fuel. It is not difficult to measure the remaining amount of fuel in a vehicle. However, with awareness of environmental protection and in order to avoid excessive dependence on oil, people have focused on electric vehicles (EVs) which have low noise, low environmental pollution, easily controlled pollution sources, and diverse kinds of energy.
Generally, EVs are drove by electrical energy stored in a battery. A charge and discharge processes with large current often exit in EVs. It is not easy to accurately measure the remaining electrical quantity of a battery and thus it is very important to manage and analyze the battery. State of charge (SOC) and state of healthy (SOH) of a battery can be reflected by variation of internal impedance of a battery. Therefore, the SOC and SOH of a battery can be measured by direct current (DC) internal impedance and a temperature of the battery. The SOC shows the remaining electrical quantity of a battery. The SOH shows a state parameter of a battery, and the state parameter is a parameter quantifying the internal impedance variation of the battery resulting from ageing phenomenon. Therefore, a user may know an appropriate time to charge and replace a battery by checking the SOC and the SOH of the battery, respectively.
A method for checking the SOH of a battery mostly uses impedance tracking technology, i.e., using DC impedance and open circuit voltage to calculate the chemistry capacity of a battery and then with assistance of a look-up table estimating the SOC and SOH of the battery. Furthermore, the open circuit voltage is not measured when a battery is in off-line state, and thus the accuracy for the SOC and SOH obtained by means of look-up table is debatable. Actually, the open circuit voltage needs to be measured when a battery is idle or has a light load. Furthermore, only in a particular charge or discharge process the capacity of a battery can be updated. That is, information regarding the SOC and SOH of a battery cannot be obtained in real time. In view of above, there has been a key problem for how to obtain the internal parameters of a battery in a real time and thus deduce the SOC and SOH of the battery.